Color display devices operating on battery power and capable of displaying color images have come to be used in portable electronic appliances, for example, by mobile phones. Color display devices used in portable electronic appliances are mostly active-matrix liquid crystal color displays using TFT devices, and there are no practical problems in terms of picture quality and display performance.
However, since such a color display device uses a white LED (light-emitting diode) in combination with color filters to achieve full color capability, a problem arises regarding color reproduction, etc. Since a white LED is used as the light source and is constructed by encapsulating a blue LED with a silicone resin containing YAG yellow phosphors to produce white light, the white color is actually blue+yellow, and is deficient in the red wavelength region. As a result, the light contains many yellow components in the red wavelength region. As for the transmission spectrum of the color filter, the color filter should have a peaky (narrowband) characteristic that allows only the specific wavelengths of blue, green, and red to pass through, but actually the color filter has a broad characteristic, allowing yellow components to pass through unattenuated, and as a result, if red is reproduced, it is rendered as yellowish red because of the presence of yellow components. Further, even if the color filter has a peaky spectral characteristic, white balance is disrupted because of the significant lack of red components in the case of the white LED light source. Furthermore, if the spectral characteristic of the color filter becomes peaky, the transmittance of the light source as a whole drops. As a result, for the color display device to retain the required brightness, an even brighter light source has to be used, resulting in an increase in power consumption of the color display device.
This has led to the development of the FSC liquid crystal color display system. As described in patent document 1, the FSC liquid crystal color display system produces a color display by emitting a plurality of light sources of different wavelengths sequentially at a rate of 60 Hz or higher and by applying drive voltage to the liquid crystal synchronized with the emission timing of each light source. The major advantages of the FSC liquid crystal color display system include the following: (1) elimination of the need for color filters contributes to greatly improving transmittance and hence reducing power consumption, (2) since the colors produced by the light sources are directly used for producing color images, a display with enhanced color reproduction can be achieved using RGB light sources having excellent emission wavelength characteristics, and (3) since there is no need to divide each pixel into segments with one for each color of the color filters, a higher resolution display can be achieved. For these and other reasons, the FSC liquid crystal color display system has been attracting attention as a liquid crystal color display system suitable for portable electronic appliances.
The FSC system, however, involves a problem called “color break-up.” This is a phenomenon in which, while the human eye tracks a moving object on the screen, RGB component images are focused at different positions on the retina of the eye (refer to patent document 2). Because of this, if the display is driven at a frequency of 60 Hz or higher, which is sufficiently faster than the response speed of the human eye, in the case of a fast-moving white object the RGB colors become visible along the boundary between the object and the background (this phenomenon will hereinafter be called the “color break-up phenomenon”). As the frame display frequency is increased above 60 Hz, the color break-up phenomenon can be gradually reduced and eventually suppressed, however in applications where a liquid crystal panel or the like is used as a light panel, there is a limit to the increase of the frame frequency, and increasing the frequency is not desirable from the standpoint of transmittance and power consumption.
In view of this, a method for alleviating the color break-up phenomenon while retaining the frame frequency of 60 Hz is proposed in patent document 2. That is, the amount of motion is calculated from the motion vector of the object, and the RGB frame images are displayed at respectively different positions so as to match the motion vector of the object, thereby alleviating the color break-up phenomenon.
On the other hand, in patent document 3, the color break-up phenomenon is alleviated by changing the order of the emitting of the RGB components from one emitting cycle to the next. For example, the emitting is performed in the order of R, G, and B in the Kth emitting cycle, in the order of G, B, and R in the (K+1)th cycle, and in the order of B, R, and G in the (K+2)th cycle. With this method, even when the frame frequency is 60 Hz, color break-up occurring on the object becomes difficult to recognize because the respective colors appear as different colors from the Kth to (K+2)th frames and are thus mixed together.
In this way, the color-breakup phenomenon can be alleviated not only by increasing the frame frequency, but also by the above proposed methods. However, while the above methods can alleviate the color-breakup phenomenon better than before, when the display is driven at a frequency of 60 Hz or higher, the color-breakup phenomenon cannot be alleviated when the frame frequency is lower than 60 Hz.
On the other hand, recent mobile phones are equipped with not only the function of displaying information on a color display device, but also the function of visually indicating the reception condition or alerting the user to the arrival of mail by emitting an LED. Some mobile phones are equipped with the function of changing the emitting color or the emitting interval of the LED to identify the source of the call or to indicate whether the received signal is for an incoming mail message or an incoming voice call.
Furthermore, in recent years, portable electronic appliances have been developed such as mobile phones that not only indicate various states of the appliance to the user by using LEDs capable of producing three RGB colors, but also produce various kinds of display effects such as illumination (decorative lighting) by programming the amount of emission of each of the three RGB colors and emitting the LEDs in various colors, for example, during voice communication. Some portable electronic appliances are designed to produce a display that attracts the attention of the user or people around him by means of illumination produced by emitting the three RGB colors in sequence, for example, when an incoming call arrives. Some portable electronic appliances produce a display that attracts the attention of the user or surrounding people, such as a display having an effect similar to that of a neon sign or illuminated advertisement like those used in a marketplace, by emitting the three RGB colors in sequence when an incoming call arrives. Further, some portable electronic appliances are designed to illuminate the entire electronic appliance by arranging several sets of LEDs capable of producing three RGB colors. As described above, portable electronic appliances that make use of three RGB color LEDs as illumination have been increasing in number.
Such illumination capability not only achieves the function of visually communicating information, but also offers the effect of greatly encouraging the user to buy the product by differentiating the product with its design and visual effects. In these circumstances, the development of products with enhanced illumination have been actively under way in recent years.    Patent Document 1: Japanese Unexamined Patent Publication No. H05-19257    Patent Document 2: Japanese Unexamined Patent Publication No. 2002-215109    Patent Document 3: Japanese Unexamined Patent Publication No. 2002-223453